This invention relates to a rolling bearing for the lengthwise guiding of a shaft or the like, comprised of an outer sleeve having axially extending races in its bore for guiding loaded rolling bodies and return races for unloaded rolling bodies. The bearing has at least one endless row of rolling bodies arranged in these races, and a sealing ring having a bore surface sliding on the shaft is provided at each end of the outer sleeve.
A rolling bearing of the above described type, in which the entire width of the bore of the sealing ring slides lengthwise along a shaft, is disclosed in DE-OS No. 2,814,917. The running friction, especially the starting friction, or initial breakaway friction of the sealing rings, is large in this rolling bearing, since these must be overcome, together with the starting friction and the inertia of the rolling bodies in the loaded and return races of the rolling bearing. As a consequence, at the beginning of lengthwise movement and also upon the reversal of lengthwise movement of the shaft from one direction into the other, larger friction peak and inertia forces occur in the rolling bearing, giving rise to noise and unsymmetrical running movements of the rolling bodies. This is of course undesirable in precision bearings, such as are provided in precision engineering.
In another known rolling bearing a sealing ring is snapped in the bore of each end ring, the sealing ring having inclined outwardly directed sealing lips sliding on the shaft (DE-AS No. 2,557,351). In this arrangement the sealing ring can cause a greater rubbing friction upon movement in one axial direction of the shaft, since the sealing ring moves inwardly as a result of the oversize of the axial friction force action on the sealing lip, and thereby the sealing lip is wedged tight between the outer ring or the housing and the shaft. As a result, under certain conditions this rolling bearing likewise can produce unsymmetrical and relatively large resistance to rolling, this is not permissable in many applications in precision machines.
The present invention therefore provides an arrangement comprising a rolling bearing for lengthwise movement along a shaft or the like, of the above type, which has satisfactory seals as well as relatively low running friction even with large oversize of the sealing ring sliding on the shaft. The respective resistance in the rolling bearing is relatively small at a start and in the reversal of the lengthwise movement of the shaft, in order to enable the use of the bearing in precision engineering and in precision machine equipment.
In the arrangement in accordance with the invention, the running friction and the inertia of the rolling body in the running and return races due to the existing acceleration is overcome at the start of the lengthwise movement of the shaft and the reversal of the lengthwise movement. When the rolling body is first brought into movement and accordingly has a low rolling friction, and the sealing lip begins to slide on the shaft, the sealing lip having a determined inclination or bending in the lengthwise direction. The clinging friction or breaking loose friction of the sealing lip shaft is thereby overcome. Since this clipping friction of the sealing lip occurs until a determined time at which the rolling bodies already have a low rolling friction, the running friction of the rolling bearing is Optimaly small upon changes in the movement in the lengthwise direction. Thereby, in an economical manner, an effective seal of the bearing space of the rolling body is insured by the sealing ring sliding on the shaft.
In another embodiment of the invention the end ring is advantageously affixed to the outer ring to compensate economically for manufacturing tolerances. In this arrangement the sealing ring is sealingly clamped fast between the end ring and the cage. The resultant resilient axial mounting of the cage of the outer sleeve also advantageously provides a noise damping action in operation.
In another embodiment of the invention, the bearing space is ventilated, so that the bow shaped bulging out of the sealing lip in the direction of change of the lengthwise movement of the shaft can be affected without being hindered by the back pressure in the inner space of the rolling bearing that inhibits bulging of the sealing lip. It is especially advantageous to provide a free space between two adjacent sealing lips on the sealing ring, with the two sealing lips being bowed to different degrees in operation.
The rolling bearing can be provided in use with relatively small disc shaped sealing rings for different applications, without requiring change of the connecting elements, such as the end ring outer ring and cage. The small space within which the sealing ring is confined, for example between the end ring and cage, is of course in many cases sufficiently small for the positioning of the elements of the rolling bearing, and therefore may be permissible in a bearing in which the sealing rings are not provided. The same rolling bearing can therefore be provided either with or without sealing rings.